This invention relates to a toner for developing latent electrostatic images used in the fields of electrophotography, electrostatic recording, and the like.
In the electrophotography and electrostatic recording, a printed or copied image can be produced, for example, by steps of forming a latent electrostatic image on a photoconductive material by a various kind of means, developing the electrostatic image with toner particles, transferring the toner which formed the image to a transferring material such as paper, Mylar film, etc., and fixing with heated rolls, pressure rolls, heated pressure rolls, or a flash light from a xenon lamp.
As toners for developing latent electrostatic images usable in the electrophotography and electrostatic recording, there have been known toners using vinyl resins as a binder such as a toner using a polystyrene resin (Japanese Patent Examined Publication No. 44-16118), a toner using a styrene-butyl methacrylate copolymer resin (Japanese Patent Examined Publication No. 56-11143), etc., a toner using a bisphenol type epoxy resin obtained by reacting a bisphenol with epichlorohydrin (Japanese Patent Unexamined Publication No. 57-96354), a toner using a polyester resin obtained by reacting a glycol having a bisphenol skeleton with a polybasic acid (U.S. Pat. No. 3,681,106) and the like. Since the vinyl resins can be controlled in wide range regarding physical properties such as molecular weight, glass transition point, melt viscosity, etc., and are very advantageous for designing toners, almost toners are obtained by using these vinyl resins.
In order to make these toners have a desirable negative charge, there are proposed processes for adding substances for imparting a negative charge to binder resins (hereinafter referred to as "negatively charging substance"), for example, a metal complex of azo compound, silica fine powder, etc. (Japanese Patent Unexamined Publication Nos. 57-130049, 57-136659, U.S. Pat. No. 4,518,673 and British Patent Laid-Open No. 2,114,310).
In order to make these toners have a desirable positive charge, there are proposed processes for adding substances for imparting a positive charge to binder resins (hereinafter referred to as "positively charging substance"), for example, nigrosine dyes (Japanese Patent Examined Publication No. 59-11901), triphenylmethane series dyes, benzoguanamine resins (Japanese Patent Unexamined Publication No. 58-192048), quaternary ammonium salts (U.S. Pat. No. 4,394,430), and processes for making the binder resins per se have a positive charge by copolymerization with positive charge imparting monomers such as vinyl pyridine (British Patent No. 1,482,905), morpholinoethyl methacrylate (Japanese Patent Unexamined Publication No. 54-41729), dialkylamioalkyl (meth)acrylates (Japanese Patent Examined Publication No. 41-9472), etc.
On the other hand, printed or copied products are sometimes stored in files containing sheets of plasticized polyvinyl chloride in order to prevent stain and damage and to use for a long period of time. But the hereto known toners using vinyl resins have a fatal defect in that when printed or copied products obtained by using such toners are stored in contact with sheets of plasticized polyvinyl chloride, the printed or copied letters and images are adhered to the sheets to produce defects of printed or copied letters and images and to make it impossible to read the letters and images.